1. Field of the Invention
The present invention relates to an optical lens. More particularly, the present invention relates to a varifocal lens formed so that to change a pressure to be applied to a liquid forming a liquid optical lens causes a curvature of an elastic light transmission membrane to be varied, thereby changing a focal distance thereof.
2. Description of the Related Art
Generally, an optical lens refers to a transparent body having at least two refractive surfaces with refractive index difference therebetween. The optical lens has been widely used in various fields such as cameras, telescopes, microscopes, etc.
For example, the optical lens is used in camera modules used in individual portable devices such as cellular phones, personal digital assistants (PDA), etc. Nowadays, the individual portable device has been developed into a multifunctional electronic device including, but not limited to, a camera function, a game function, a music playing function, a broadcasting function, an internet function, etc. in addition to a simple voice transmitting/receiving function. Therefore, the individual portable devices are required to integrate many functions in a small space.
Also, for acquiring better images the camera module has been formed to have an auto focus function, an auto zoom function, an auto macro function, an anti-shake function, etc. However, the camera module having the various advanced functions as described above is limited to reduce a size thereof because of sizes of lenses, and a size of a mechanical lens driving apparatus.
In other words, the various advanced functions are required to have many kinds of lenses, such as macro lenses (close-up lenses), standard lenses, telephoto lenses, zoom lenses, etc. Then, a lens mounted on the camera module needs to be replaced by other lens according to its usage. The auto focus function is required to adjust an optical characteristic of the lens, that is, a focal distance of the lens so that separate motor and driver are required to adjust the focal distance. As a result, the camera module having the advanced functions inevitably has a large size. So to use the camera module having the various advanced functions in the individual portable device smaller in size is difficult.
For solving this problem, liquid lenses (fluid lenses) have been developed using an electrowetting phenomenon.
In the liquid lens, a surface tension of the liquid is changed according to voltage, and the change of the surface tension causes the curvature of the lens to be varied. So, the auto focus function and the zoom function can be realized. The curvature of the liquid lens is varied by the electrowetting phenomenon. The liquid lens using the electrowetting phenomenon is not required to mechanically move the lens so that the camera module can be formed smaller in size.
Furthermore, there is another kind liquid lens configured to change a pressure of a liquid. The liquid lens changes a pressure applied to an optical liquid filled in a lens chamber, thereby changing a curvature of an elastic light transmission membrane disposed in the lens chamber. So the auto focus function and the zoom function of the liquid lens can be realized. This type liquid lens also needs no mechanical lens movement so that the camera module can be formed smaller in size.
However, a varifocal lens using a method applying a pressure to a liquid is substantially affected by gravity. Therefore, the varifocal lens has a limitation of the size to be manufactured.